Sleep disorders in Parkinson's disease (PD) have received increasing attention in the recent literature. Studies have reported a variety of disturbances of sleep and arousal in PD including insomnia, daytime somnolence and rapid eye movement sleep behavior disorder (RBD). Some sleep disorders have been reported to precede the onset of motor symptoms in PD by a number of years and are related to the neurodegenerative process of the disease. In addition, the presence of cognitive impairments in PD has been established. Although disturbances of sleep and arousal have long been associated with neuropsychological functioning and quality of life, no studies have examined the association of sleep disturbances with cognitive deficits in PD. A key factor in investigating etiology of PD is the side of motor symptom onset. Studies have found distinct cognitive and motor symptom profiles between PD patients with right and left side disease onset. Thus, the first aim of the proposed study is to further examine sleep problems in PD and to investigate whether there are differences in PD patients with right and left side symptom onset with regard to sleep and arousal disturbances. The second aim of this study is to investigate how sleep problems and daytime drowsiness are related to cognitive functioning and quality of life in PD. The study will examine sleep parameters in PD patients and age-matched normal control adults (NC) using a self-report sleep scale, a self-report sleepiness scale, two actigraphs that will monitor motor activity during the 24-hour sleep-wake cycle, and a sleep diary. Participants will receive a comprehensive neuropsychological assessment and their activities of daily living will be reviewed. These methods will allow investigation of sleep behaviors in patients with PD and will give further insight into the etiology of their cognitive deficits by examining how sleep and arousal disturbances are related to cognition and are impacted by the side of motor symptom onset in this patient population. PUBLIC HEALTH RELEVANCE: Sleep disturbances and cognitive impairment are among the non-motor manifestations of PD that adversely impact the quality of life of patients and their caregivers, but are often overlooked by clinicians. Because some sleep disorders appear to be harbingers of PD, gaining insight into sleep and its association with cognition may possibly lead to earlier detection and management of the disease